Method of fabricating a finned heat exchanger



Se t. 7, 1937. R. w. KRITZER ET AL,

METHOD OF FABRICATING A FINNED HEAT EXCHANGER Filed Dec. 31, 1935 2Sheets-Sheet 1 FIGZ ' INVENTORS.

FIG. 3

p ,1937. R. w. KRITZER HAL 2,092,110

METHOD OF FABRICATING A FINNED'HEAT EXCHANGER Filed Dec. 31, 1935 2Sheets-Sheet 2 J I'NVENTOPS a w /5. FIIIGJZ".

Patented Sept. 7, 1937 UNITED STATES PATENT OFFICE Application December31, 1935, Serial No. 56,936

.lClaim.

One of the objects of our invention is to fabricate a finned heatexchanger of continuous tubing, the parallel reaches of which are placedat very close centers.

Another of the objects of our invention is to provide a finned heatexchanger in which the tubing is firmly gripped by the fins.

A further object of our invention is to provide a finned heat exchanger,which necessitates a minimum amount of labor and machinery for thefabrication of the same.

Further objects of our invention include a finned heat exchanger havinga very high rate of heat absorption.

Referring to the drawings:

Figure 1 is an isometric view, looking upward, of a fin coil embodyingour invention.

Figure 2 is an elevational view of a fin as used in our invention.

Figure 3 is a plan view of a fluid conduit used in our invention.

Figure 4 is a vertical cross-section along line A-A, Figure 1.

Figure 5 is a cross-section along line BB,

Figure 4.

Figure 6 is a cross-section of a return bend of the fluid conduit,Figure 3.

Figure 7 is a cross-section along line CC, Figure 6.

Figure 8 is a cross-section along line D--D,

Figure 6.

Figure 9 is a modification of the fluid conduit shown in Figure 3.

Figure 10 is another modification of the fluid a5 conduit shown inFigure 3.

Figure 11 is a cross-section along lines EE and F-F of Figures 9 and 10,respectively.

Figure 12 is a diagrammatic illustration showing a certain manner ofpressing the tubing into 40 the fin apertures.

In the drawings:

Figure 1, a finned tube heat exchanger I, comprises a fluid conduit 2having an inlet 3 and an outlet 4, between both of which are a 45'plurality of parallel reaches joined by return bends 5. Upon theparallel reaches .oi'the fluid conduit 2, and between the oppositereturn bends 5, a multiplicity of spaced apart fins 6 have a frictionalengagement with thefluid conduit 2.

50 The upper edges, of the fins 6, have slots I which frictionallyengage longitudinal bracing bars 8 driven into the slots.

. In Figure 2, a metallic fin plate 6 has slots 1 in each right-hand andleft-hand upper corner.

55 The lower portion of the fin plate 6 has spaced return bends 5, issqueezed to a smaller dimension, at certain points, than the dimensionof the conduit at the parallel reaches. The reason 10 therefor will befully explained later.

In Figures 4 and 5, the lower portion, of a fluid conduit 2, isflattened-with ridges ii! angularly disposed relative to the length ofthe parallel reaches of the fluid conduit 2. Fluid wells l5 l3 liebetween adjacent ridges l2.

In Figures 6, 7 and 8, the return bend 5 is formed, in a suitablebender, so that the section (J-C is of comparatively elliptical form,for a purpose to be explained later, and the section 20 DD is left ofsubstantially its former shape, prior to the bending operation. Thepurpose of the change in section along lines D--D, as com- I pared tothe section of C-C, is because that in bending thin walled tubing, to ashort radius 25 and without the aid of internal devices for preventinginward buckling of the tube walls during the bending operation, the tubewalls at the inner radius of the bend will buckle inwardly, unless theaccumulated stresses are released at 30 given points. We have found thatbending dies, made to all the humps shown at D-D, to form during thebending operation, allow us to form copper tubing, of .032 thick walls,to commercially acceptable return bends of radius to the center of thetube.

In Figures 9 and 10, we show return bends II, which are of the samecross-section as the tubing prior to bending. These return bends, onshort radius bends, are generally made with internal former mandrels,during the bending operation, to prevent buckling of the tube walls atthe bends.

In Figure 11 is shown a cross-section-of the conduit along lines E-E ofFigure 9 and lines F -F of Figure 10.

In Figures 7 and 11, the cross-sections shown should have a width lessthan the dimension of the openings ID of the apertures 9 of the finplate 6, Figure 2.

Having described the elements of the invention, we shall now describethe method of fabricating a coil in accordance with the invention.

Using outside diameter copper tubing, we bend it, with suitable dies asmentioned previu ously, to the form shown in Figure 3.

, to use we punch the apertures 9 with a round die having a diameter of.640", which is .015 larger than the outside diameter of the tubingused. The fin ,plate fi is so positioned in respect to the punching diethat the aperture irbreaks' through the edge of the fin plate 6, asshown'in Figure 2, and produces an opening l0, which is approximately.531" 'in width.

Laying the formed conduit 2, of Figure 3, upon a flat surface, we thenengage the return bends 5, at the right-hand side of FigureB, at thelines C of Figure 6, with the openings ID of the apertures 9 of the finplate 6, Figure 2.

Since the openings ID are wider than the width In placing'the fins alongthe conduit, in their' proper spacedrelationship, We employ spacers,which we prefer made of a hardwood although any suitablematerial may beemployed.

After the coil is assembled, we have a series of spaced fins, with aspacer. between adjacent fins. We now pass the assembly to a pressingmachine, which is illustrated diagrammatically in Figure 12, in which astationary table 15 provides a support for the finned tube heatexchanger I, which is step moved along in the direction indicated by thearrow. A die I6, hav: ing projections II onits working face, movedup anddown at intervals, presses the tubing conduit 2 to a D shape havingangularly disposed ridges along the fiat portion of the D shape as shownin Figures 1, 4 and 5 In pressing the tubing to a D shape, the tubing ispressed against the sides of the apertures '9 of the fin plates 6, andthe fin plates 6 are firmly gripped by the conduit 2.

After the conduit tube 2 is pressed into all of the fins, the spacers,between adjacent fin plates 6, are then removed and the longitudinalbracing bars 8 are then driven into the slots I, which rigidifies theupper edges of the fins 8, making a comparatively solid assembly.

In certain cases, we may prefer to have return bends having a full tubecross-section and, in that case, we shall form the bends as shown inFigure 9, in which the section EE is slightly flattened to a dimensionless than .531", allowing the fin plates to drop. onto, the conduit atthese flattened portions, from which they can 1) moved to theirrespective positions.

In other cases, we may prefer to assemble the finsand spacers in aseparate jig and then lay the conduit tube 2 into the assembly, engagingall the fin, plates 6 simultaneously, without the necessity of movingthe pin plates to their respective positions after dropping them ontothe tube at the flattened sections. In this case, we shall fiatten theentire length of the parallel reaches. joined by the return bends, asshown in Figure 2, to a dimension less than .531", which is the width oftheopening II) in the fin plates 6, Figure 2.

While we have described preferred forms of the invention, it isunderstood that departures from the same may be employed withoutdeparting from the spirit and scope of the invention, which is limitedonly to the following claim.

We claim:

The method of manufacturing a. heat exchanger which comprises preforminga conduit with parallel courses joined by return bends,

punching fin plates with apertures breaking through an edge of the finplates, the said apertures having a narrower width at the said edge thanthe aperture width at some point within the said fins, deforming thesaid conduit to a width-v

